1. Field
One embodiment of the invention relates generally to a disk drive and, in particular, to a disk drive for perpendicular magnetic recording.
2. Description of the Related Art
In general, a disk drive representative of a hard disk drive is adapted to, when data is recorded on a disk medium, generate a timing signal called a write gate and output data (write data) from a read/write channel to a head amplifier in response to an output timing of the write gate. The head amplifier converts the write data to a write signal (write current) and outputs it to a head (see, for example, JPN. PAT. APPLN. KOKAI PUBLICATION NO. 2004-295985).
Here, due to a delay of, for example, a circuit constituting a read/write channel, a write signal is output from a head, actually, in a way to be delayed from an output timing point of a write gate and is recorded as data onto the disk medium. At this time, that delayed portion is recorded as a write splice (WS) on the disk medium. This write splice section serves as an area recorded immediately prior to a preamble serving as a header of the write data. The record pattern of the write splice section provides a direct current (DC) pattern of no magnetic inversion.
In recent years, a disk drive of a perpendicular magnetic recording system has been practically adopted. In such a disk drive, if the above-mentioned write splice section is present, the reproduced waveform from a read head becomes a DC-offset waveform due to the filter characteristic of the head amplifier. Upon being input to the read/write channel, the reproduced waveform exerts an adverse effect on the signal processing for reproducing the recorded data.
In the read/write channel, the acquisition operation of a PLL circuit is effected by the preamble of the reproducing signal. In this case, under an influence of the DC offset reproduction waveform, the acquisition operation of the PLL circuit becomes unstable by the preamble, thus presenting a situation of causing a delay of the acquisition operation.